Electrical measuring instrument



Jan. 10, 1928.

W. E. HULL ELECTRICAL MEASURING INSTRUMENT ATTORNEYS INVENTOR 15'. H 111 L Walter Filed April 14. 1926 WITNESSES 7% M Patented Jan. 10, 1928.

1,656,116 PATENT OFFICE.

WALTER E. HULL, 0F SHARPSVILLE, PENNSYLVANIA.

ELECTRICAL MEASURING INSTRUMENT.

Application filed April 14,1926. ser al Ho..101,993.

This invention relates to improvements in electrical measuring instruments, an object being to provide a simple instrument for quickly'determining or measuring the ohmic resistance of any given conducting. elementwithout requiring any setting of rheostats by hand or any of the performances usually required in ascertaining an unknown resistance.

Other objects and advantages will appear.

in the following specification, reference being had to the accompanying drawing, in

which a Figure 1 is a front elevation of the'irnproved electrical measuring instrument, a portion of the casing being broken away to reveal the internal arrangement. Figure 2 is a side elevation of ment.

Figure 3 is a central section taken on the line 3-3-of Figure 1. I I Fi re 4 is an elevation of the coils,pointer and. rame hereinafter referred to.

Figure 5 is a detail perspective view of the' pointer.

the instru- Fi re 6 is a detail perspective view of the rame.

As briefly indicated in the foregoing statements of the object of the invention, the mstrument is des1gned for measurlng an unknown electrical resistance with the same facility that the current of an electr cal C11- cuit can be measured with the familiar ammeter or the electrical pressure can be measlid till

ured with a volt meter. The instrument is so arranged that it may qulckly be applied and the quantity of the unknown resistance read in ohms. o

In carrying out the invention provislon 1s made of a wood or other suitable base 1 upon which the frame 2 is mounted by means of screws 3 or other suitable fastening devices. These pass through holes in the flanges 4 with which the frame is provided. The frame is formedto produce a tubular portion 5 (Fig. 6), the ends of which come to points or are oppositely beveled asat 7. Diametrically oppositely beveled sides are parallel to each other so that coils of wire may be wound upon the tubular portion in crossed arrangement. M i The tubular frame portion or form' 5 is preferably taped (ordinary friction tape be-. mg used) prior to winding the code 8 and 9 in order'to furnish desirable insulation. The

coil 8 is composed of wire 'of slightly greater diameter than that of the coil 9 thereby, because its res1stance to current is less, producing a stronger magnetic field around the coil 8 when the coils are energized and when {hie unknown resistance is zero as explained I a er.

'Binding posts 10 and 11 provide cqnnections-for the remote ends of the coils 8 and 9, while a single central binding post 12 re.- vides the connection for the near ends 0 the coils which are joined as at 13. Current is derived from a source of energy, for examplethe battery B. The positive pole of the battery is connected with the binding post 11 by means ofa wire 14". The negative pole of the battery is connected with the binding post 12 by means of a wire 15. The remain- .ing binding post 10 is connected with the positive pole of the battery by means of a mm; 16, but the unknown resistance '17 which is-to be measured is interposed in this .wire as diagrammatically illustrated in Fig These elements are assembled at rightangles upon the axle 20, the ends of which'are finely pointed to revolve as freely as possible in bearings 21 on the interior of the tubular form 5 of the frame. The pointer is counterbalanced as at 22 so that it may not be affected by gravity, should the instrument not be sitting in a level position. The pointer is movable over a dial 23 which is graduated in ohms as indicated at 24. The dial is secured upon the base. The entire instrument is protected b a cover 25 which has an arouate slot 26 tirough which the end of the pointer and the graduation can be observed.

The operation is readily understood. The coils 8 and 9 which may be said to constitute a cruciform coil having separate crossed windings of relatively different resistance capacity are so wound upon the tubular form 5 that a passage of current through the coil 8 will produce north and south poles asindicated by the small abbreviations N and S in Figure 4. The coil 9 is so wound that a passage of current therethrough will the current in both coils was the same.

However, the coil 8 is of wire of slightly greater diameter, as has been stated, and an ual E. M. F. impressed across both coils zt he resistance in the branch 16 being regarded as zero) will produce a slight rotation of the resultant magnetic field of the coils to the left so that the pointer 19 assumes an initial zero position in reference to the dial 23. The magnetic needle 18 lies in .the direction of the lines of force and will follow the. resultant of the magnetic fields at the coils.

Assume that an unknown resistance 17 is to be measured. The resistance is interposed in the branch 16 between the positive-pole of the battery B and the binding 0st 10 of the relatively heavy wire coil 8. he interposition of the resistance reduces the current delivered to the coil 8 and inv turn weakens the magnetic field thereof so that the resultant of the magnetic forces of the two coils rotate to the right. The magnetic needle 18-follows, and the pointer 19 traverses the dial 23to the right. The amount of movement of the needle and of the pointer 19 to the right increases as the resistance 17 increases.

Ordinarily .a simple dry cell is employed as the electrical current source B. The current in the positive branch 14 is substanthrough the two coils remains th tiall constant, but is variable in the branch 16 ue'to the inter osition of the resistance to be measured. lf the resistance 17 is eliminated so that the current in both branches 14 and 16 is balanced, the needle 19 will be caused to take the initial zero position over the dial 23 in the manner pre viously stated. But an increase in resistance by reason of insertion of resistance 17 will result in a decrease of the electro-magnetic field of the coil 8 and a rotation of the resultant field to the right with a consequent movement of the pointer 19 to the right. The position of the pointer 19 will not be affected by the strength of the dry cell, assuming the dry cell to become weaker with use, as the proportion of the currents flowing gardless of the stren Instruments of t may be designed to measure very hi h or very lowresistances,the only difference ein in the requirement of different coils to suit the various purposes. A few turns of wire of relatively large, diameter are used for measuring low resistances, and many turns of wire of ,much less diameter are used for measuring high resistances. It is also unh of the cell.

c same re-' e foregoing character cation or measure;

While the construction and arrangement of the improved ielectrical measurin instrument is that of a generally re erred form, obviously modifications an may be made without departing from the spirit of the invention or the scope of the claims.

, I claim 1. An electrical measuring instrument comprising a cruciform 0011 having separate crossed windings of relatively different resistance magnitudes and a source of constant E. for both coils, an indicator and a magnetic needle armature occupying and pivotally mounted in the electro-magnetic field of. the coils, said armature causing the needle to swin to a zero indicating position, determine by the resultant of the magnetic fields of the unbalanced coils when subject to the constant E. M. F. aforesaid, and being swung to an ohm-indicating position by the shifting of said resultant through interposition in the said unbalanced coil circuits of an n own resistance whose magnitude is determined by the proportionate movement of the indicator armature responsive to the shifting of said resultant.

2. An electric' measuring instrument comprising a pair of coils in crossed relationship and of relatively different resistance magnitudes, a source of constant E. M. F. having connections with one end of each of the coils and with the joined other ends of the coils, an indicator and a magnetic needle armature occupying and pivotally mounted in the electro-magnetic field of said coils, the movement of the magnetic needle to zero indicating position being coincident with and dependent upon the normal unbalanced condition of the electro-inagnetic field through a constant E. M, F. impressed across both coils, rovision being made for interposing an un own resistance between the current source and that coil of loss resistance ma iitude to vary the resistance and thereby s lift the resultant of the magnetic fields of the coils and the indicator armature in proportion to the amount of the unknown resistance interposed in the circuit.

3. In an electric measuring instrument a tubular coil mounting having top, bottom and sides closed and integral and having its ends open and provided with offset supportg ing brackets atthe bottom thereof, the opposite sides ofthe mounting being each oppositely beveled outwardly to substantial] a point with diametrically opposed beve s changes rate crossed windings, alined trunnion hearings on and projecting inwardly from the inner faces of said tubular mounting approximately at right angles to the axis of the electro-magnetic fields of said coils, and an armature consisting of a magnetic needle trunnioned in said bearings.

4. An electric measuring instrument comprising a cruciform coil having separate crossed windings of relatively different resistance magnitudes and a source of constant E M. F. with connections providing for separate circuits of constant E. M. F. ifor each coil, an indicator and a magnetic needle armature occupying and pivotally mounted in the electro-magnetic field of the coils, said armature causing the needle to be swung to a zero indicating position determined by the resultant of the electromagnetic field oi the unbalanced coils when subjected to the constant B. M. F. aforesaid, and being swung to an ohm-indicating position by the shifting oi said resultant through the interposition in the circuit of the coil of less resistance magnitude of an unknown resistance whose magnitude is determined by the proportionate movement of the indicator armature responsive to such shifting of the resultant.

' WALTER 1E. HULL. 

